The present invention relates to improved overlay or bond coatings applied to materials used in the hot sections of modern gas turbine engines.
Thermal barrier coatings on a substrate alloy usually include a thermally insulating ceramic layer deposited over a metallic bond coat. Traditionally, thermal barrier coatings use yttria partially stabilized zirconia on a bond coat such as MCrAlY delivered by a low pressure plasma spray, air plasma, or physical vapor deposition method. A typical thermal barrier coating for a rotating airfoil application consists of the metallic bond coat over a single crystal casting of a nickel based alloy. On the bond coat, the thermally insulating layer is deposited typically by electron beam physical vapor deposition. The ceramic adheres to the bond coat through the formation of a thin, thermally grown oxide scale of aluminum oxide. During engine operation, the thermally grown oxide grows. Attendant with the growth of the oxide scale are increased thermally grown oxide residual stresses and bond coat creep.
Thus, there is needed an overlay bond coat which has improved strength, particularly creep strength, and which would lead to improved thermal barrier coating life.
Accordingly, it is an object of the present invention to provide a bond coating which has improved strength properties.
It is a further object of the present invention to provide a method for forming an improved overlay bond coating having improved strength properties.
The foregoing objects are attained by the overlay coatings and the deposition method of the present invention.
In accordance with the present invention, an improved overlay coating is provided. The overlay coating comprises a deposited layer of MCrAlY material containing discrete nitride particles therein. The overlay coatings of the present invention may also include dispersed oxide particles as well as dispersed nitride particles.
A method for forming an overlay coating on a substrate material, such as a component used in a hot section of a gas turbine engine, broadly comprises depositing a MCrAlY coating on a substrate material and forming a plurality of discrete nitride particles in the coating. The nitride particles are preferably formed using a controlled introduction of nitrogen during the deposition step. After the overlay or bond coating with the dispersion particles have been formed, a thermal barrier coating may be formed over the overlay or bond coating.
Other details of the thermal barrier coating through the application of dispersion strengthened metallic bond, as well as other objects and advantages attendant thereto, are set forth in the following detailed description.